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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10 Sep 2025, at 22:14, Andrew Zaborowski wrote: > Handling a memory failure pointing inside a huge page requires splitting > the page. The splitting logic uses a mechanism, implemented in > migrate.c:try_to_map_unused_to_zeropage(), that inspects contents of > individual pages to find zero-filled pages. The read access to the > contents may cause a new, synchronous exception like an x86 Machine > Check, delivered before the initial memory_failure() finishes, ending > in a crash. > > Luckily memory_failure() already sets the has_hwpoisoned flag on the > folio right before try_to_split_thp_page(). Don't enable the shared > zeropage mechanism (RMP_USE_SHARED_ZEROPAGE flag) down in > __split_unmapped_folio() when the original folio has has_hwpoisoned. > > Note: we're disabling a potentially useful feature, some of the > individual pages that aren't poisoned might be zero-filled. One > argument for not trying to add a mechanism to maybe re-scan them later, > apart from code cost, is that the owning process is likely being > killed and the memory released. Sounds reasonable to me. > > Signed-off-by: Andrew Zaborowski > --- > mm/huge_memory.c | 3 ++- > mm/memory-failure.c | 6 ++++-- > 2 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9c38a95e9f0..1568f0308b9 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3588,6 +3588,7 @@ static int __folio_split(struct folio *folio, unsig= ned int new_order, > struct list_head *list, bool uniform_split) > { > struct deferred_split *ds_queue =3D get_deferred_split_queue(folio); > + bool has_hwpoisoned =3D folio_test_has_hwpoisoned(folio); The state needs to be stored here because __split_unmapped_folio() clears the flag. Maybe add a comment here to prevent people from =E2=80=9Coptimizing=E2=80=9D it by calling folio_test_has_hwpoisoned(f= olio) in the code below. (I wanted to until I checked the definition of folio_test_has_hwpoisoned()) > XA_STATE(xas, &folio->mapping->i_pages, folio->index); > struct folio *end_folio =3D folio_next(folio); > bool is_anon =3D folio_test_anon(folio); > @@ -3858,7 +3859,7 @@ static int __folio_split(struct folio *folio, unsig= ned int new_order, > if (nr_shmem_dropped) > shmem_uncharge(mapping->host, nr_shmem_dropped); > > - if (!ret && is_anon) > + if (!ret && is_anon && !has_hwpoisoned) > remap_flags =3D RMP_USE_SHARED_ZEROPAGE; > remap_page(folio, 1 << order, remap_flags); > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index fc30ca4804b..2d755493de9 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -2352,8 +2352,10 @@ int memory_failure(unsigned long pfn, int flags) > * otherwise it may race with THP split. > * And the flag can't be set in get_hwpoison_page() since > * it is called by soft offline too and it is just called > - * for !MF_COUNT_INCREASED. So here seems to be the best > - * place. > + * for !MF_COUNT_INCREASED. > + * It also tells __split_unmapped_folio() to not bother s/__split_unmapped_folio/__folio_split/, since remap_page() is called in __folio_split(). > + * using the shared zeropage -- the all-zeros check would > + * consume the poison. So here seems to be the best place. > * > * Don't need care about the above error handling paths for > * get_hwpoison_page() since they handle either free page > --=20 > 2.45.2 Otherwise, Acked-by: Zi Yan Best Regards, Yan, Zi